This invention is in the field of sewing machines, more particularly, it pertains to bobbin thread run-out indicators for sewing machines.
There are in the prior art many forms of bobbin thread run-out indicators, which indicators are invariably concerned with indicating a low bobbin thread condition or an empty bobbin condition. A low bobbin thread indicator is desirable in order to warn an operator of impending bobbin exhaustion which might interfere with the appearance of a long seam. An empty bobbin indicator would provide a warning to an operator to avert operation of the sewing machine with no thread remaining on the bobbin.
However, it frequently occurs that when the bobbin is wound, too much thread can be placed thereon, resulting in some cases in thread spillage and/or in a binding of the bobbin. There have been proposed mechanical devices designed to prevent overwinding of the bobbin. Such a device is shown in the U.S. Pat. No. 3,154,035, issued on Oct. 27, 1964 to Edwards et al. In this device a thread engaging shoe was deflected by a full thread condition of a winding bobbin into a bobbin driver causing a drag on the sewing machine during bobbin winding in order to advise an operator that the bobbin was fully wound. There is also the U.S. Pat. No. 3,138,127, issued on June 23, 1964 to Ketterer, which provided a thread engaging member which deflected the bobbin driver upon a full thread condition of the bobbin, which deflection was sensed through a microswitch arrangement detecting motion at the end of the bobbin driver shaft, thereby turning off the sewing machine. None of these prior art devices, however, provided for also sensing for a low bobbin condition with an indication to an operator thereof.
What is required is a sewing machine which will provide an indication to an operator of a low bobbin thread condition indicating the need to initiate bobbin winding; and, upon a full bobbin condition, provide an indication to an operator thereof.